1. Technical Field
The present disclosure relates to a method for switching communication methods, a communication system, a base station, a transmitter and a receiver, and more particularly, to a method for switching communication connection modes, a communication system, a base station, a transmitter and a receiver.
2. Description of Related Art
With widespread of mobile broadband applications and demands for transmitting massive amounts of data, resource of radio spectrum has become increasingly scarce. In order to solve said problem, technique of creating available bandwidths from space domain has been developed. Thus, 3rd Generation Partnership Project (3GPP) has been focusing on feasibility of supporting Device-to-Device (D2D) communication in Long Term Evolution-Advanced (LTE-A) standard and the establishment of system requirements. The D2D communication is a new technique which allows User Equipments (UE) to directly communicate with adjacent UEs by using licensed bands or unlicensed bands (for example, Wireless Local Area Networks (WLAN)) in conjunction with heterogeneous networks after proximity discovery under the control of a wireless communication system. The D2D communication technique may increase a system spectral efficiency and reduce a transmitted power of each terminal, so as to solve the problem of scarce resource of radio spectrum in the wireless communication system. In addition, the D2D communication technique may also satisfy requirements of proximity communications, such as electronic flyers and alarm systems, in some commercial applications and during disaster relief.
FIG. 1A illustrates a cellular communication method of conventional art. As shown in FIG. 1A, when a UE 110 intends to transmit data to an UE 120, the data can only be transmitted to the UE 120 after being sequentially forwarded by a base station 130, a network entity 140 and a base station 150. In other words, a traditional cellular communication connection is used between the UEs 110 and 120 for transmitting the data.
When a distance between the UEs 110 and 120 is reduced to fall within a specific range, the base station 130 (or the base station 150) may then switch a communication method between the UEs 110 and 120 to a D2D communication as shown in FIG. 1B.
FIG. 1B is a schematic view illustrating a conventional device-to-device communication. It could be observed from FIG. 1B that the UEs 110 and 120 may transmit the data to each other without forwarding the data via the base station 130, the network entity 140 and the base station 150, thereby achieving an effect of network offloading.
Further, when the base station 130 (or the base station 150) determines that the UEs 110 and 120 cannot continue the D2D communication for being too far from each other, the communication method between the UEs 110 and 120 may still be switched back to the traditional cellular communication connection as shown in FIG. 1A.
Based on a system requirement of the D2D communication defined by the 3GPP, it is required that the LTE-A has capabilities in establishing the D2D communication connection for one UE, controlling radio sources used in the D2D communication connection, and switching the communication connections between the D2D communication connection and the traditional cellular communication connection without affecting quality of service (QoS).
In the LTE-A, a bearer is responsible for transmitting the data between two network entities. A data stream between the UE and Packet Data Network Gateway (P-GW) is transmitted by an Evolved Packet System (EPS) bearer.
FIG. 2 is a schematic diagram of a data stream between a plurality of network entities in the conventional LTE-A. The network entities include, for example, the UE, Evolved Node B (eNB), Serving Gateway (S-GW), Packet Data Network Gateway (P-GW) and Peer Entity. Among these network entities, the UE and the eNB belong to, for example, Evolved Universal Terrestrial Radio Access Network (E-UTRAN), and the S-GW and the P-GW belong to, for example, Evolved Packet Core (EPC). The Peer Entity is, for example, a network entity that performs an end-to-end service with the UE.
As shown in FIG. 2, EPS radio bearer (RB) is a logic bearer formed by serially connecting three entity bearer including radio bearer, S1 bearer, and S5/S8 bearer. When each EPS radio bearer is established, the P-GW may configure a set of corresponding QoS parameters, and the eNB may schedule the data streams in different EPS Radio Bearers according to the QoS parameters, so as to meet QoS requirements. With respect to the UE, the data streams having the different QoS requirements may use different EPS radio bearers for achieving different quality of services. Therein, the radio bearer is responsible for transmitting the data between the eNB and the UE, and radio bearer includes Packet Data Convergence Protocol (PDCP) layer and Radio Link Control (RLC) layer. When the EPS radio bearer is established with more stringent requirement in Packet Error loss Rate (PELR), the eNB may use the Acknowledge Mode (AM) to transmit the data at a RLC entity of the corresponding radio bearer (i.e., a retransmitting mechanism of Automatic Repeat-reQuest (ARQ) is operated at the RLC layer).
However, when the communication method between the UEs is switched from the cellular communication connection to the D2D communication connection, it is obvious that the radio bearers between the eNB and the UEs are no longer suitable in use for the D2D communication connection. In this case, how to meet the more stringent requirement in the Packet Error loss Rate (PELR) during process of switching from the traditional cellular communication connection to the D2D communication connection is indeed an important issue to be solved.